In hot-dip metal plating equipment, to adjust the thickness of hot-dip metal (zinc or the like) plating applied to a steel plate, wiping nozzles which face each other are disposed, one on a front surface side of the steel plate and the other on aback surface side thereof, and gas jets are blown onto the front surface and the back surface of the steel plate from these wiping nozzles.
Each of the above-described wiping nozzles has an internal space formed into a passage chamber for a compressed gas, and has a shape extended in a plate-width direction of a steel plate. In addition, a lip (a blowing port for the gas jet) in a front end of the wiping nozzle has the shape of a slit extending in the plate-width direction of the steel plate and is also designed to be longer than the plate width of the steel plate.
At opposite end portions of the steel plate in the plate-width direction, a disturbance occurs in the jet flow due to collision of the gas jets, which are blown out from the wiping nozzles facing each other as described above. This disturbance causes edge-overcoating, in which the plating becomes thicker on the edges than on and around a center portion of the steel plate in the plate-width direction, and splashing, in which the hot-dip metal scatters.
In view of this, there is a technique in which baffle plates are disposed at the opposite end portions of the steel plate in the plate-width direction, thereby reducing the edge-overcoating and the splashing. This technique is effective if the distance between each end portion of the plate and the corresponding baffle plate is set at 5 mm or less. However, since the steel plate as being passed meanders by approximately ±50 mm at a maximum, it is necessary to control the positions of the baffle plates such that the baffle plates follow the meandering but do not come into contact with the plate end portions with such a precision as to keep the distance from the plate end portions at approximately 5 mm or less. However, increasing the production speed also increases the speed of meandering, preventing the baffle plates from following the meandering. As a result, an accident in which the plate comes into contact with the baffle plate is likely to occur.
In view of this, Patent Documents 1 to 3 listed below disclose techniques to reduce edge-overcoating and splashing without using baffle plates.